Flowmeter with resistor heater

ABSTRACT

An air temperature detector  12  is disposed close to an auxiliary passage sidewall  15 , which has an auxiliary passage wall hole  9  formed near the air temperature detector  12 . A heat-sensitive resistor  13  is also disposed close to the auxiliary passage sidewall  15 , which has an auxiliary passage wall hole  10  formed near the heat-sensitive resistor  13 . Further, a resistor heater  14  is disposed close to an auxiliary passage sidewall  16 , which has an auxiliary passage wall hole  11  near the resistor heater  14.

TECHNICAL FIELD

The present invention relates to an air flowmeter with a resistor heaterfor measuring the amount of intake air flowing through an intake passageof an internal combustion engine, and more particularly to a flowmeterwith a resistor heater, which is suitable for measuring the flow rate ofair sucked into an automobile engine.

BACKGROUND ART

It is known that conventional flowmeters with resistor heaters havevarious measurement errors. One of those measurement errors is atemperature characteristic error that occurs upon a detecting device,such as a resistor heater, heated by heat transmitted through astructure of the flowmeter with the resistor heater. Heat generatingsources typically include 1) an engine and an exhaust pipe, and 2) apower transistor forming a signal amplification circuit in an electroniccircuit section of the flowmeter with the resistor heater. There arepossibly two heat transmission routes, i.e., A) one along which heat istransmitted through the structure of the flowmeter with the resistorheater and then directly reaches the detector, and B) the other alongwhich heat is transmitted through the structure of the flowmeter withthe resistor heater to raise the temperature of an auxiliary passagewall, whereby the temperature of an airflow in contact with theauxiliary passage wall rises and resulted heat reaches the detectingdevice.

When heat is transmitted to a temperature sensor for measuring an airtemperature, the temperature detected by the temperature sensor ishigher than the ambient air temperature by the amount of heattransmitted to the temperature sensor, and the amount of the transmittedheat directly produces an error of the measured temperature. When heatis transmitted to a resistor heater, the necessity of electricallyheating the resistor heater is reduced in the amount of heat detected bythe detecting device, and the output of the flowmeter with the resistorheater is reduced correspondingly. This is because the flowmeter withthe resistor heater operates such that the temperature of the resistorheater is controlled to be always held at a fixed value higher than thetemperature of a heat-sensitive resistor at all times and an electricpower required for that control is taken out as a measured value. Whenheat is transmitted to the heat-sensitive resistor, the amount by whichthe resistor heater must be heated is increased in the amount of heatreceived by the detecting device, and the output of the flowmeter withthe resistor heater is increased correspondingly. In such a way,heat-induced errors occur in the flowmeters with the resistor heaters.

In the conventional flowmeters with resistor heaters, it is known toreduce or adjust the thermal effect upon the detecting device, such asthe resistor heater, through structural members as disclosed in, e.g.,JP, A 60-36916. Further, in the flowmeter disclosed in JP, A 60-36916,the shape and the material of a terminal supporting the detecting deviceare changed for adjustment of the thermal effect from the structuralmembers.

DISCLOSURE OF THE INVENTION

However, the solution of changing the shape and the material of theterminal accompanies problems, such as a deterioration of weldabilitywith the detecting device when the material of a detecting devicesupport is changed, and a reduction of productivity when the support hasa complicated structure.

An object of the present invention is to provide a flowmeter with aresistor heater, which has increased productivity.

To achieve the above object, the present invention provides a flowmeterwith a resistor heater, comprising a detector for detecting an air flowrate, a heat-sensitive resistor for measuring an ambient temperature tocompensate a heated temperature of the detector, and an auxiliarypassage in which the detector and the heat-sensitive resistor arearranged, wherein a hole is formed in a wall of the auxiliary passagenear each or one of the detector and the heat-sensitive resistor.

With that construction, an influence of temperature upon the detector orthe heat-sensitive resistor can be reduced just by changing the positionof the hole, and productivity can be improved.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal seeing-through sectional view showing anoverall construction of a flowmeter with a resistor heater according toone embodiment of the present invention.

FIG. 2 is a longitudinal sectional view of an auxiliary passage of theflowmeter with the resistor heater according to one embodiment of thepresent invention.

FIG. 3 is a longitudinal seeing-through sectional view showing aprincipal construction of the flowmeter with the resistor heateraccording to one embodiment of the present invention.

FIG. 4 is a plan view of a principal part of the flowmeter with theresistor heater according to one embodiment of the present invention.

FIG. 5 is a longitudinal sectional view of the auxiliary passage of theflowmeter with the resistor heater according to one embodiment of thepresent invention.

FIG. 6 is a longitudinal sectional view of the auxiliary passage of theflowmeter with the resistor heater according to one embodiment of thepresent invention.

FIG. 7 is a longitudinal sectional view of the auxiliary passage of theflowmeter with the resistor heater according to one embodiment of thepresent invention.

FIG. 8 is an explanatory view for explaining the effect of reducing aninfluence of temperature in the flowmeter with the resistor heateraccording to one embodiment of the present invention.

FIG. 9 is an explanatory view for explaining the effect of reducing aninfluence of temperature in the flowmeter with the resistor heateraccording to one embodiment of the present invention.

FIG. 10 is an explanatory view for explaining the effect of reducing aninfluence of temperature in the flowmeter with the resistor heateraccording to one embodiment of the present invention.

FIG. 11 is an explanatory view for explaining the effect of reducing aninfluence of temperature in the flowmeter with the resistor heateraccording to one embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The construction of a flowmeter with a resistor heater according to oneembodiment of the present invention will be described below withreference to FIGS. 1 to 11.

First, a description is made of an overall construction of the flowmeterwith the resistor heater according to one embodiment of the presentinvention with reference to FIGS. 1 and 2.

FIG. 1 is a longitudinal seeing-through sectional view showing theoverall construction of the flowmeter with the resistor heater accordingto one embodiment of the present invention, and FIG. 2 is a longitudinalsectional view of an auxiliary passage of the flowmeter with theresistor heater according to one embodiment of the present invention,i.e., a sectional view taken along the line A—A in FIG. 1.

As shown in FIG. 1, a module housing 4 of the flowmeter with theresistor heater is mounted to an intake passage 1 of an automobileinternal combustion engine through a module flange 3. A connector 2 forelectrical connection to the exterior is provided on the module flange3. An auxiliary passage 6 is formed in a fore end portion of the modulehousing 4. An air temperature detector 12, a heat-sensitive resistor 13,and a resistor heater 14 are disposed within the auxiliary passage 6.

A part of air sucked to the internal combustion engine through theintake passage 1 flows into the auxiliary passage 6 through an auxiliarypassage inlet 7 and then flows out to the intake passage 1 through anauxiliary passage outlet 8. The temperature of the air having flown intothe auxiliary passage 6 is detected by the air temperature detector 12.The flow rate of the air having flown into the auxiliary passage 6 isdetected by the resistor heater 14, and the temperature of the intakeair is compensated using the heat-sensitive resistor 13.

The air temperature detector 12, the heat-sensitive resistor 13, and theresistor heater 14 are electrically connected to an electronic circuitdisposed within the module housing 4. The electronic circuit isconnected to the exterior through the connector 2 and outputs a detectedsignal of the air flow rate and a detected signal of the air temperatureto the exterior. The electronic circuit disposed within the modulehousing 4 is enclosed by a cover 5 in a sealed condition.

Then, as shown in FIG. 2, the air temperature detector 12 is disposedclose to an auxiliary passage sidewall 15, which has an auxiliarypassage wall hole 9 formed near the air temperature detector 12. Theheat-sensitive resistor 13 is also disposed close to the auxiliarypassage sidewall 15, which has an auxiliary passage wall hole 10 formednear the heat-sensitive resistor 13. Further, the resistor heater 14 isdisposed close to an auxiliary passage sidewall 16, which has anauxiliary passage wall hole 11 near the resistor heater 14.

Moreover, as shown in FIG. 2, the air temperature detector 12 and theheat-sensitive resistor 13 are both arranged on the same plane withrespect to an airflow X. On the other hand, the resistor heater 14 isarranged downstream of the air temperature detector 12 and theheat-sensitive resistor 13 in the direction of the airflow X on a planedifferent from the plane on which the air temperature detector 12 andthe heat-sensitive resistor 13 are both arranged. Because of the airtemperature detector 12 and the heat-sensitive resistor 13 eachdetecting the temperature of the inflow air, if the resistor heater 14is arranged upstream of them, the temperature detection cannot beaccurately performed with the presence of heat generated by the resistorheater 14. For that reason, the resistor heater 14 is arrangeddownstream of the air temperature detector 12 and the heat-sensitiveresistor 13. Also, if a device disturbing the airflow is arrangedupstream of the resistor heater 14, the air flow rate cannot beaccurately measured. For that reason, the resistor heater 14 is arrangedon the plane different with respect to the airflow X from the plane onwhich the air temperature detector 12 and the heat-sensitive resistor 13are both arranged.

Next, the dimensions and shapes of the auxiliary passage wall holesformed in the flowmeter with the resistor heater according to thisembodiment will be described with reference to FIGS. 3 and 4.

FIG. 3 is a longitudinal seeing-through sectional view showing aprincipal construction of the flowmeter with the resistor heateraccording to one embodiment of the present invention, and FIG. 4 is aplan view of a principal part of the flowmeter with the resistor heateraccording to one embodiment of the present invention. Note that the samecharacters in FIGS. 1 and 2 denote the same components.

As shown in FIG. 3, the auxiliary passage wall holes 9, 10 and 11 eachhave a shape of a rectangular slit. Then, as shown in FIGS. 3 and 4,each of the auxiliary passage wall holes 9, 10 and 11 formedrespectively near the air temperature detector 12, the heat-sensitiveresistor 13 and the resistor heater 14 has a transverse width L2 that isset not smaller than a transverse width L1 of each of the airtemperature detector 12, the heat-sensitive resistor 13 and the resistorheater 14 (L2≧L1), but not greater than a width L3 of the auxiliarypassage 6 (L2≦L3). Incidentally, the auxiliary passage wall holes 9, 10and 11 are each not limited to a slit shape, and may be formed into, forexample, an elliptic or circular shape.

The above-described construction in which the air temperature detector12, the heat-sensitive resistor 13, and the resistor heater 14 arearranged in the auxiliary passage 6 causes two problems as follows.

-   1) When detecting devices, such as the air temperature detector 12,    the heat-sensitive resistor 13 and the resistor heater 14, are    disposed close to the auxiliary passage walls 15, 16, the airflow    flowing through the auxiliary passage 6 passes primarily through an    area in which flow resistance is relatively small, and therefore the    flow rate of the air flowing between the detecting device and the    auxiliary passage wall tends to reduce to a very small value. Such a    tendency reduces the effect of cooling the detecting device heated    by heat coming from the exterior or heat generated by a power    transistor section of the control circuit, which is achieved with    the airflow flowing through the auxiliary passage.-   2) Since the heat transmitted from the exterior or the power    transistor section is transmitted through structural members of the    air flowmeter, the temperature of the auxiliary passage wall itself    also rises. With this regard, the airflow flowing through the    auxiliary passage 6 while contacting the auxiliary passage walls 15,    16 is heated and the temperature of the air residing within a    certain distance from each auxiliary passage wall rises. An area in    which the air temperature rises is gradually enlarged starting from    a most upstream end point of the auxiliary passage wall. If the    detecting device, such as the resistor heater, is disposed within    the area in which the air temperature rises, an error due to    temperature occurs as in the case where the heat transmitted through    the structural members directly raises the temperature of the    detecting device.

Next, a description is made of the dimensions and shapes of theauxiliary passage wall holes according to this embodiment, which aresuitable for enhancing the cooling effect by increasing the flow speedso as to cancel off a decrease of the cooling effect described in theabove (1), with reference to FIG. 5.

FIG. 5 is a longitudinal sectional view of the auxiliary passage of theflowmeter with the resistor heater according to one embodiment of thepresent invention. Note that the same characters in FIGS. 1 to 4 denotethe same components.

To increase the flow speed of the airflow flowing between the airtemperature detector 12 and the auxiliary passage wall 15, the auxiliarypassage wall hole 9 formed near the air temperature detector 12 isoffset a distance m1 downstream of the air temperature detector 12 inthe direction of the airflow in the auxiliary passage 6. The offsetamount m1 means the distance between the center of the air temperaturedetector 12 and the center of the auxiliary passage wall hole 9 in thedirection of the airflow. By forming the auxiliary passage wall hole 9with the offset distance m1 in the downstream direction of the airflowin the auxiliary passage 6, a part of the air flowing in through theauxiliary passage inlet 7 is caused to flow out through the auxiliarypassage wall hole 9. As a result, the flow rate of the air flowingbetween the air temperature detector 12 and the auxiliary passage wall15 increases and so does the flow speed of the air around the airtemperature detector 12. It is hence possible to increase the effect ofcooling the detecting device heated by, e.g., heat coming from theexterior, which is achieved with the airflow flowing through theauxiliary passage.

Likewise, to increase the flow speed of the airflow flowing between theheat-sensitive resistor 13 and the auxiliary passage wall 15, theauxiliary passage wall hole 10 formed near the heat-sensitive resistor13 is offset a distance m2 downstream of the heat-sensitive resistor 13in the direction of the airflow in the auxiliary passage 6. By formingthe auxiliary passage wall hole 10 with the offset distance m2 in thedownstream direction of the airflow in the auxiliary passage 6, the flowrate of the air flowing between the heat-sensitive resistor 13 and theauxiliary passage wall 15 increases and so does the flow speed of theair around the heat-sensitive resistor 13. It is hence possible toincrease the effect of cooling the detecting device heated by, e.g.,heat coming from the exterior, which is achieved with the airflowflowing through the auxiliary passage.

Further, to increase the flow speed of the airflow flowing between theresistor heater 14 and the auxiliary passage wall 16, the auxiliarypassage wall hole 11 formed near the resistor heater 14 is offset adistance m3 downstream of the resistor heater 14 in the direction of theairflow in the auxiliary passage 6. By forming the auxiliary passagewall hole 11 with the offset distance m3 in the downstream direction ofthe airflow in the auxiliary passage 6, the flow rate of the air flowingbetween the resistor heater 14 and the auxiliary passage wall 16increases and so does the flow speed of the air around the resistorheater 14. It is hence possible to increase the effect of cooling thedetecting device heated by, e.g., heat coming from the exterior, whichis achieved with the airflow flowing through the auxiliary passage.

The offset amounts m1, m2 and m3 are each set to be, e.g., in the rangeof −1 mm to +3 mm. Here, the sign (+) means the offset amount in thedownstream direction of the airflow from the detecting device, and thesign (−) means the offset amount in the upstream direction of theairflow from the detecting device. The offset amounts m1, m2 and m3 mustbe each changed depending on the dimension, etc. of the detectingdevice, and a practical example of those offset amounts will bedescribed later with reference to FIG. 7.

Next, a description is made of the dimensions and shapes of theauxiliary passage wall holes according to this embodiment, which aresuitable for dividing a temperature boundary layer to avoid thetemperature error caused by a temperature rise of the auxiliary passagewall described in the above (2), with reference to FIG. 6.

FIG. 6 is a longitudinal sectional view of the auxiliary passage of theflowmeter with the resistor heater according to one embodiment of thepresent invention. Note that the same characters in FIGS. 1 to 4 denotethe same components.

To reduce the effect of heat of the auxiliary passage wall 15, thetemperature boundary layer is divided such that the heat generated fromthe auxiliary passage wall 15 will not be transmitted to the airtemperature detector 12. To that end, an auxiliary passage wall hole 9′formed near the air temperature detector 12 is offset a distance n1upstream of the air temperature detector 12 in the direction of theairflow in the auxiliary passage 6. The offset amount n1 means thedistance between the center of the air temperature detector 12 and thecenter of the auxiliary passage wall hole 9′ in a direction opposed tothe direction of the airflow. By forming the auxiliary passage wall hole9′ with the offset distance n1 in the upstream direction of the airflowin the auxiliary passage 6, the temperature boundary layer is divided bythe air flowing in through the auxiliary passage wall hole 9′ so thatthe heat from the auxiliary passage wall 15 is less transmittable to theair temperature detector 12. As a result, it is possible to reduce theinfluence of the heat from the auxiliary passage wall 15 and to lowerthe temperature of the air around the detecting device.

Likewise, to reduce the influence of the heat from the auxiliary passagewall 15 upon the heat-sensitive resistor 13, an auxiliary passage wallhole 10′ formed near the heat-sensitive resistor 13 is offset a distancen2 upstream of the heat-sensitive resistor 13 in the direction of theairflow in the auxiliary passage 6. By forming the auxiliary passagewall hole 10′ with the offset distance n2 in the upstream direction ofthe airflow in the auxiliary passage 6, the temperature boundary layeris divided by air flowing in through the auxiliary passage wall hole 10′so that the heat from the auxiliary passage wall 15 is lesstransmittable to the heat-sensitive resistor 13. As a result, it ispossible to reduce the influence of the heat from the auxiliary passagewall 15.

Further, to reduce the influence of the heat from the auxiliary passagewall 16 upon the resistor heater 14, an auxiliary passage wall hole 11′formed near the resistor heater 14 is offset a distance n3 upstream ofthe resistor heater 14 in the direction of the airflow in the auxiliarypassage 6. By forming the auxiliary passage wall hole 11′ with theoffset distance n3 in the upstream direction of the airflow in theauxiliary passage 6, the temperature boundary layer is divided by airflowing in through the auxiliary passage wall hole 11′ so that the heatfrom the auxiliary passage wall 16 is less transmittable to the resistorheater 14. As a result, it is possible to reduce the influence of theheat from the auxiliary passage wall 16.

The offset amounts n1, n2 and n3 are each set to be, e.g., in the rangeof 0 mm to +5 mm. Here, the sign (+) means the offset amount in theupstream direction of the airflow from the detecting device. The offsetamounts n1, n2 and n3 must be each changed depending on the dimension,etc. of the detecting device, and a practical example of those offsetamounts will be described later with reference to FIG. 7.

Next, a description is made of the dimensions and shapes of theauxiliary passage wall holes according to this embodiment, which aresuitable for overcoming the above-described problems (1) and (2), withreference to FIG. 7.

FIG. 7 is a longitudinal sectional view of the auxiliary passage of theflowmeter with the resistor heater according to one embodiment of thepresent invention. Note that the same characters in FIGS. 1 to 6 denotethe same components.

The auxiliary passage wall hole 9 formed near the air temperaturedetector 12 is offset the distance m1 downstream of the air temperaturedetector 12 in the direction of the airflow in the auxiliary passage 6to increase the flow speed of the airflow flowing between the airtemperature detector 12 and the auxiliary passage wall 15. With thisarrangement, the flow rate of the air flowing between the airtemperature detector 12 and the auxiliary passage wall 15 is increased,thus enabling the airflow flowing through the auxiliary passage to coolthe air temperature detector 12 heated by, e.g., heat coming from theexterior.

Assuming here that the length L1(12) of the air temperature detector 12is 2.5 mm and the width L3 of the auxiliary passage 6 is 9.5 mm, thetransverse width L2(9) of the auxiliary passage wall hole 9 is set to9.5 mm so as to satisfy the relationship of L1(12)≦L2(9)≦L3.

Also, assuming that the air temperature detector 12 has a cylindricalshape with a diameter φ12 of 1.0 mmφ and the auxiliary passage wall hole9 has a height H(9) of 1.0 mm, the offset amount m1 is set to +0.5 mm.

The auxiliary passage wall hole 10 formed near the heat-sensitiveresistor 13 is offset the distance m2 downstream of the heat-sensitiveresistor 13 in the direction of the airflow in the auxiliary passage 6to increase the flow speed of the airflow flowing between theheat-sensitive resistor 13 and the auxiliary passage wall 15. With thisarrangement, the flow rate of the air flowing between the heat-sensitiveresistor 13 and the auxiliary passage wall 15 is increased, thusenabling the airflow flowing through the auxiliary passage to cool theheat-sensitive resistor 13 heated by, e.g., heat coming from theexterior.

Assuming here that the length L1(13) of the heat-sensitive resistor 13is 2.0 mm and the width L3 of the auxiliary passage 6 is 9.5 mm, thetransverse width L2(10) of the auxiliary passage wall hole 10 is set to8.5 mm so as to satisfy the relationship of L1(13)≦L2(10)≦L3.

Also, assuming that the heat-sensitive resistor 13 has a cylindricalshape with a diameter φ13 of 0.8 mmφ and the auxiliary passage wall hole10 has a height H(10) of 1.5 mm, the offset amount m2 is set to +2.5 mm.

The auxiliary passage wall hole 11′ formed near the resistor heater 14is offset the distance n3 upstream of the resistor heater 14 in thedirection of the airflow in the auxiliary passage 6 to divide thetemperature boundary layer by air flowing in through the auxiliarypassage wall hole 11′. With this arrangement, the heat from theauxiliary passage wall 16 is less transmittable to the resistor heater14, and the influence of the heat from the auxiliary passage wall 16 canbe reduced.

Assuming here that the length L1(14) of the resistor heater 14 is 2.0 mmand the width L3 of the auxiliary passage 6 is 9.5 mm, the transversewidth L2(11′) of the auxiliary passage wall hole 11′ is set to 8.5 mm soas to satisfy the relationship of L1(14)≦L2(11′)≦L3.

Also, assuming that the resistor heater 14 has a cylindrical shape witha diameter φ14 of 0.5 mmφ and the auxiliary passage wall hole 11′ has aheight H(11′) of 1.0 mm, the offset amount n3 is set to +2.5 mm.

Stated another way, in the example shown in FIG. 7, the auxiliarypassage wall holes 9, 10 are formed to be offset respectively thedistances m1, m2 downstream of the air temperature detector 12 and theheat-sensitive resistor 13 in the direction of the airflow in theauxiliary passage 6, whereby the detectors 12, 13 are cooled by the airflowing through the auxiliary passage. On the other hand, the auxiliarypassage wall hole 11′ formed near the resistor heater 14 is offset thedistance n3 in the upstream direction of the airflow in the auxiliarypassage 6, whereby the influence of the heat from the auxiliary passagewall 16 is reduced.

Next, a description is made of the effect of reducing the influence oftemperature, which is resulted from the construction shown in FIG. 7,with reference to FIGS. 8 to 11.

FIGS. 8 to 11 are each an explanatory view for explaining the effect ofreducing the influence of temperature in the flowmeter with the resistorheater according to one embodiment of the present invention.

FIGS. 8 and 9 show distributions of air flow speed depending on theabsence and presence of the auxiliary passage wall holes 9, 10, and theyshow results of analyzing distributions of air flow speed in theauxiliary passage, which were obtained by verifying the effect of theauxiliary passage wall holes with the CAE analysis.

FIG. 8 shows the flow speed distribution resulting in the absence of theauxiliary passage wall holes 9, 10. As shown in FIG. 8, when noauxiliary passage wall holes are formed near the air temperaturedetector 12 and the heat-sensitive resistor 13, the air flow speed ismuch lower in the gaps formed between the air temperature detector 12and the heat-sensitive resistor 13 and the auxiliary passage wall 15, towhich those detecting devices are positioned close, than in a centralarea of the auxiliary passage 6. Therefore, the effect of cooling theair temperature detector 12 and the heat-sensitive resistor 13, which isachieved with the airflow flowing through the auxiliary passage, isreduced by half.

On the other hand, FIG. 9 shows the flow speed distribution resultingwhen the auxiliary passage wall holes 9, 10 are formed. With thepresence of the auxiliary passage wall holes 9, 10 near the airtemperature detector 12 and the heat-sensitive resistor 13, as shown inFIG. 9, the airflow is caused to flow into the auxiliary passage wallholes 9, 10 formed in the auxiliary passage wall 15 near the airtemperature detector 12 and the heat-sensitive resistor 13 in such a waythat relatively fast airflows contact substantially overall peripheriesof both the detecting devices. As a result, the effect of cooling theair temperature detector 12 and the heat-sensitive resistor 13, which isachieved with the airflow flowing through the auxiliary passage, isincreased.

Further, FIGS. 10 and 11 show temperature distributions depending on theabsence and presence of the auxiliary passage wall hole 11′, and theyshow results of analyzing distributions of air temperature in theauxiliary passage 6, which were obtained by verifying the effect of theauxiliary passage wall hole with the CAE analysis. FIG. 10 shows theflow speed distribution resulting in the absence of the auxiliarypassage wall hole 11′.

As shown in FIG. 10, when no auxiliary passage wall hole is formed nearthe resistor heater 14, the airflow flowing through the auxiliarypassage 6 is heated by the auxiliary passage wall 16, which is in turnheated by heat coming from the exterior or generated by the electroniccircuit, and then forms a flow having high temperature in the vicinityof the auxiliary passage wall 16. The airflow thus heated by theauxiliary passage wall 16 reaches the resistor heater 14. Consequently,the resistor heater 14 is affected by the heat from the auxiliarypassage wall 16, thereby causing an error due to temperature.

On the other hand, FIG. 11 shows the temperature distribution resultingwhen the auxiliary passage wall hole 11′ is formed. With the presence ofthe auxiliary passage wall hole 11′ near the resistor heater 14, asshown in FIG. 11, an airflow generated in the vicinity of the auxiliarypassage wall 16 and having high temperature is divided by the auxiliarypassage wall hole 11′. As a result, the temperature of the airflowaround the resistor heater 14 lowers and the influence of the heat fromthe auxiliary passage wall 16 can be reduced.

In the example described with reference to FIG. 7, the auxiliary passagewall holes 9, 10 and 11′ are each formed into a shape of a rectangularslit. However, those auxiliary passage wall holes may have an ellipticshape. Practical dimensions in such a case will be described below.

The auxiliary passage wall hole 9 is formed into an elliptic shape witha major radius of RL(9) and a minor radius of Rs(9). Assuming that thelength of the air temperature detector 12 is L1(12) and the width of theauxiliary passage 6 is L3, the respective dimensions are set so as tosatisfy the relationship of L1(12)≦RL(9)≦L3. The offset amount m1 is setto be in the range of −1 mm to +3 mm.

Also, the auxiliary passage wall hole 10 is formed into an ellipticshape with a major radius of RL(10) and a minor radius of Rs(10).Assuming that the length of the heat-sensitive resistor 13 is L1(13) andthe width of the auxiliary passage 6 is L3, the respective dimensionsare set so as to satisfy the relationship of L1(13)≦RL(10)≦L3. Theoffset amount m2 is set to be in the range of −1 mm to +3 mm.

Further, the auxiliary passage wall hole 11′ is formed into an ellipticshape with a major radius of RL(11) and a minor radius of Rs(11).Assuming that the length of the resistor heater 14 is L1(14) and thewidth of the auxiliary passage 6 is L3, the respective dimensions areset so as to satisfy the relationship of L1(13)≦RL(11′)≦L3. The offsetamount n3 is set to be in the range of 0 mm to +5 mm.

When the auxiliary passage wall hole has a circular shape, therespective dimensions can be set by assuming the major radius RL(9)=theminor radius Rs(9), the major radius RL(10)=the minor radius Rs(10), andthe major radius RL(11′)=the minor radius Rs(11′) in the above-describedcase in which the auxiliary passage wall hole has an elliptic shape.

With this embodiment, as described above, temperature characteristics ofthe flowmeter with the resistor heater can be improved only with thepassage structure of the flowmeter without improving a flow ratemeasuring device of the flowmeter with the resistor heater and withoutadding a special electronic circuit for compensation.

Also, by modifying combination of the size and the position of the holeformed near each detecting device, temperature characteristics of theflowmeter with the resistor heater can be easily adjusted. Therefore,optimum temperature characteristics can be simply obtained regardless ofthe construction of the flowmeter with the resistor heater, as well asthe shape and temperature conditions of the intake passage of theautomobile internal combustion engine.

Further, the flowmeter with the resistor heater can be manufactured at acost comparable to that of a conventional flowmeter with a resistorheater without changing the method of manufacturing the conventionalflowmeter.

It is to be noted that the present invention is effective to not onlythe above-described measurement of an airflow, but also to measurementof other fluids, such as hydrogen, nitrogen or water.

INDUSTRIAL APPLICABILITY

According to the present invention, productivity of the flowmeter withthe resistor heater can be improved.

1. A flowmeter, comprising: a heat-sensitive resistor a heat-radiatingdevice, controlled according to heat sensed by said heat-sensitiveresistor, such that heat radiated by said heat-radiated device isrepresentive of air flow rate, wherein said heat-sensitive resistormeasures an ambient temperature to compensate for a heated temperatureof said heat-radiating device, an auxiliary passage in which saidheat-radiating device and said heat-sensitive resistor are arranged andthrough which a part of air flowing through an intake passage flows inand out, and a module housing defining said auxiliary passage; whereinthe module housing has a sidewall extending in a direction of flow ofsaid part of air flowing through said intake passage; and wherein a holeis formed in the sidewall of said module housing for communication ofsaid auxiliary passage with said intake passage near each of or one ofsaid heat-radiating device and said heat-sensitive resistor.
 2. Aflowmeter according to claim 1, further comprising: a temperature sensorarranged in said auxiliary passage and measuring a fluid temperature,and a hole formed in the sidewall of said module housing near saidtemperature sensor.
 3. A flowmeter according to claim 2, wherein saidheat-radiating device, said heat-sensitive resistor, and saidtemperature sensor are disposed inside said auxiliary passage closer tothe sidewall of said module housing than to a central axis of saidauxiliary passage.
 4. A flowmeter according to claim 3, wherein each ofsaid holes increases a flow speed of an airflow flowing around acorresponding one of said heat-radiating device, said heat-sensitiveresistor, and said temperature sensor.
 5. A flowmeter according to claim4, wherein a central position of each of said holes is arranged withinthe range of −1 to +3 mm relative to a central axis of saidheat-radiating in a downstream direction of said auxiliary passage.
 6. Aflowmeter according to claim 1, wherein each of said holes divides atemperature boundary layer generated in an airflow contacting with thesidewall of said module housing in said auxiliary passage.
 7. Aflowmeter according to claim 6, wherein a central position of each ofsaid holes is arranged within the range of 0 to +5 mm relative to acentral axis of said heat-radiating device in an upstream direction ofsaid auxiliary passage.
 8. A flowmeter according to claim 2, wherein,assuming that each of said heat-radiating device, said heat-sensitiveresistor and said temperature sensor has a transverse width of L1 andsaid auxiliary passage has a rectangular sectional shape with a width ofL3, a transverse width L2 of each of said holes satisfies L1≦L2≦L3.
 9. Aflowmeter, comprising: a heat-sensitive resistor, a heat-radiatingdevice controlled according to heat sensed by said heat-sensitiveresistor, such that heat radiated by said heat-radiated device isrepresentative of air flow rate, wherein said heat-sensitive resistormeasures an ambient temperature to compensate for a heated temperatureof said heat-radiating device, an auxiliary passage in which saidheat-radiating device and said heat-sensitive resistor are arranged, anda module housing defining said auxiliary passage, wherein said flowmeteris mounted to an intake passage by inserting said module housing intosaid intake passage, said auxiliary passage has an inlet for allowingair flow from said intake passage into said auxiliary passage and anoutlet for allowing air flow from the inside of said auxiliary passageto said intake passage, a length of air flow axially through saidauxiliary passage is greater than a length of air flow axially throughsaid intake passage bypassing said auxiliary passage, the module housinghas a sidewall extending in a direction of flow of said air flowing fromsaid intake passage into said auxiliary passage; and a hole is formed inthe sidewall of said module housing near each of or one of saidheat-radiating device and said heat-sensitive resistor.
 10. A flowmeter,comprising: a resistor heater, a heat-sensitive resistor for measuringan ambient temperature to compensate a heated temperature of saidresistor heater, an auxiliary passage in which said resistor heater andsaid heat-sensitive resistor are arranged and through which a part ofair flowing through an intake passage flows in and out, and a modulehousing defining said auxiliary passage; wherein the module housing hasa sidewall extending in a direction of flow of said part of air flowingthrough said intake passage; wherein a hole is formed in the sidewall ofsaid module housing for communication of said auxiliary passage withsaid intake passage near each of or one of said resistor heater and saidheat-sensitive resistor; wherein a part of said module housing isinserted through an inserting hole of said intake passage, and saidauxiliary passage is arranged in said intake passage; and wherein asectional area of said inserting hole is smaller than a sectional areaof said auxiliary passage.
 11. A flowmeter according to claim 10,further comprising: a temperature sensor arranged in said auxiliarypassage and measuring a fluid temperature, and a hole formed in thesidewall of said module housing near said temperature sensor.
 12. Aflowmeter according to claim 11, wherein said resistor heater, saidheat-sensitive resistor, and said temperature sensor are disposed insidesaid auxiliary passage closer to the sidewall of said module housingthan to a central axis of said auxiliary passage.
 13. A flowmeteraccording to claim 12, wherein each of said holes increases a flow speedof an airflow flowing around a corresponding one of said resistorheater, said heat-sensitive resistor, and said temperature sensor.
 14. Aflowmeter according to claim 13, wherein a central position of each ofsaid holes is arranged within the range of −1 to +3 mm relative to acentral axis of said resistor heater in a downstream direction of saidauxiliary passage.
 15. A flowmeter according to claim 11, wherein,assuming that each of said resistor heater, said heat-sensitive resistorand said temperature sensor has a transverse width of L1 and saidauxiliary passage has a rectangular sectional shape with a width of L3,a transverse width L2 of each of said holes satisfies L1 ≦L2 ≦L3.
 16. Aflowmeter according to claim 10, wherein each of said holes divides atemperature boundary layer generated in an airflow contacting with thesidewall of said module housing in said auxiliary passage.
 17. Aflowmeter according to claim 16, wherein a central position of each ofsaid holes is arranged within the range of 0 to +5 mm relative to acentral axis of said resistor heater in an upstream direction of saidauxiliary passage.